Pressure actuated electrical bypass circuit for a high voltage bushing

ABSTRACT

A bushing having an electrical contact mounted within an insulating housing, the electrical contact being supported in a position to receive the electrically conductive probe on a high voltage terminator, an electrical bypass circuit element mounted in the housing for completing an electrical circuit between the probe and the electrical contact in the bushing whenever the pressure of the gas produced by the heat of the prestrike arc on fault close-in produces a sufficient force against the electrical contact to break a frangible member allowing the pressure of the gas to move an element rapidly away from the probe and into electrical engagement with the bypass member. A pressure responsive clamp is also provided in the bushing to clamp the probe in the bushing.

United States Patent Flatt May 20, 1975 PRESSURE ACTUATED ELECTRICALPrimary Examine rRoy Lake BYPASS CIRCUIT FOR A HIGH VOLTAGE AssistantExaminer-DeWalden W. Jones BUSHING Attorney, Agent, or FirmRonald E.Barry [75] Inventor: Richard P. Flatt, Oconomowoc.

w [57] ABSTRACT [73] Assigneez RTE Corporation, Wankesha, A bushinghaving an electrical contact mounted within an insulating housing, theelectrical contact being sup- Filedi 14, 1974 ported in a position toreceive the electrically conduc- [21] Appl. N0.: 451,167 tive probe on ahigh voltage terminator, an electrical bypass circuit element mounted inthe housing for completing an electrical circuit between the probe and[52] US. Cl. 339/111; 200/144 C the electrical Contact i the bushingwhenever the Int. i pressure of the gas produced the heat of the pre-Field of Seal'Ch 339/l 1 i 143 R, 143 strike arc on fault close-inproduces a sufficient force 200/144 R, 149 A against the electricalcontact to break a frangible member allowing the pressure of the gas tomove an References Cited element rapidly away from the probe and intoelectri- UNITED STATES PATENTS cal engagement with the bypass member. Apressure 3,509,516 4 1970 Phillips 339 111 x responsive Clamp is alsoProvided in the bushing I9 3,586,802 6/1971 Nichols et a1. 200/144 cclamp the probe in the g- 3,654,59O 4/1972 Brown 339/111 18 Claims, 4Drawing Figures PATENTED HAY 2 0 I975 SHEET 10F 2 PRESSURE ACTUATEDELECTRICAL BYPASS CIRCUIT FOR A HIGH VOLTAGE BUSHING Background of theInvention In high voltage underground power distribution systemselectrical termination is achieved by the manual movement of electricalcontacts into engagement. When the open contacts are moved towardengagement with one another, an arc will form between the contactsbefore they actually come into engagement due to the high voltagebreaking down the insulation air between the contacts. When the contactsare located in a confined space, a substantial danger exists thatequipment may be excessively damaged or an operator may be injured as aresult of the pressure of the gases developed in the interval betweencontact prestrike and electrical engagement of the contacts. This dangeris heightened when gas evolving arc quenching materials are locatedadjacent the movable contacts. Under normal operating conditions, manualoperation of the movable contacts in a power distribution system isgenerally satisfactory because the arc is not severe. However, aninherent danger in such systems is that a short circuit may be presenton the system at the time of close-in. Under short circuit conditions,an abnormally high are current would be created during the prestrikeinterval and prior to the electrical engagement of the contacts and thisare would usually develop enough gas to either throw one of the contactstoward the operator, or cause an explosion of the contact assembly.

Summary of the Invention The present invention relates to a bushing forconnecting an electrical apparatus to the conductive probe of a highvoltage terminator. The bushing is provided with a frangible member toconfine the gases developed during contact prestrike within the bushingso that the force of the gas can be used to complete an electricalbypass circuit between the bushing and terminator. In one embodiment,when the force of the gas pressure acting on the bushing contact exceedsthe strength of the frangible member, the frangible member will breakallowing the contact to move rapidly inwardly into the bushing intoelectrical engagement with the bypass circuit and thereby immediatelyextinguish the arc between the probe and the contact. In anotherembodiment, when the force of the gas pressure exceeds the strength ofthe frangible member, the frangible member will rupture forcing aconductive member into en gagement with a conductive cylinder tocomplete the bypass circuit.

Drawings FIG. 1 is a side view in section showing the bushing of thisinvention with the conductive probe shown at the entrance to the bushingand spaced from the element;

FIG. 2 is a view similar to FIG. 1 showing the position of the elementafter the frangible disc has been broken by the pressure of the gasdeveloped on prestrike;

FIG. 3 is a view of another embodiment of the invention with theconductive probe at the entrance to the bushing; and

FIG. 4 is a view similar to FIG. 3 showing the frangible element afterrupture and closing of the bypass circuit.

Description of the Invention The bushing 10 of the present invention isused to connect the conductive probe or contact 12 ofa terminator 14 toan electrical apparatus. A high voltage electrical connector assembly ofthis type is shown in US. Pat. No. 3,474,386 of Edwin A. Link entitledElectrical Connector, issued on Oct. 21, 1969. In this type of aconnector assembly, a gas evolving arc-quenching extension or rod 16 isprovided on the end of the probe 12 and a gas evolving arc-quenchingsleeve 18 is provided on the end of the conductive sleeve or contact 20within the bushing 10. The are quenching material can be any of the wellknown arc extinguishing materials such as hard vulcanized fiber, theacrylics and polytetrafluoroethylene. The prestrike are produced onclosein of the terminator 14 with the bushing will produce anarc-quenching gas between the extension 16 and sleeve 18 which willextinguish the are under normal operating conditions. However, undershort circuit conditions the pressure of the arc-quenching gas producedcan create an explosive condition within the bushing 10.

The bushing 10 of this invention is provided with an electrical bypassarrangement that is gas actuated to rapidly connect the sleeve 20 to theprobe 12 whenever the gas pressure exceeds a predetermined limitdetermined by a frangible member within the bushing 10. Moreparticularly, the bushing 10 includes a housing 24 formed or molded froma dielectric material and having an axially extending passage 26. Thepassage 26 is closed at one end by means of an electrically conductivecap 28 mounted on a supporting sleeve 29. The cap 28 is provided with athreaded section 31 for connecting the bushing to an electricalapparatus. An arcquenching gas evolving sleeve 30 is provided at theopen end of the passage 26.

Means are provided in the bushing 10 for rapidly connecting the probe 12to the sleeve 20 in the form of an electrically conductive cylindricalbypass member 22 provided within the passage 26 on the inner end of thesleeve 30. The member 22 includes a reduced diameter opening 32 at theinlet end for engaging the probe 12 and an opening 34 at the other endfor electrically engaging the element 20.

The sleeve or element 20 includes a number of slots 21 around the openend and a reduced diameter cylindrical section 40 at the inner end whichextends through the opening 34 in the bypass member 22. The cylindricalsection 40 is closed by means of an end wall 42 and is connected to thecap 28 by means of a flexible electrically conductive wire 44. It shouldbe noted that the sleeve 20 is free to slide axially within the tube 18from an operating position as seen in FIG. 1 to the electrical bypassposition shown in FIG. 2.

In this regard, the sleeve or element 20 is supported for slidingmovement within the bypass element by means of the insulating tube 18which is positioned with the bypass member 22. The tube 18 includes areduced diameter opening 38 at the inlet end for engaging the extension16 and an enlarged diameter section 39 around the open end of sleeve 20.The tube in the normal position of the sleeve or element 20 insulatesthe sleeve 20 from the bypass member 22.

The sleeve 20 is retained in the operating position by means of afrangible insulator 46 provided at the inner end of the passage 26 inthe bushing housing 24. The

frangible insulator 46 includes a cylindrical section 48 which ispositioned within the passage 26 and a cylindrical section 50 connectedto the cylindrical section 48 by means of a frangible section or ring52. The cylindrical section 50 has an inside diameter substantiallyequal to the outside diameter of the cylindrical section 40 on thesleeve 20. The section 40 is inserted into the reduced diameter section50 until the end 54 of the section 50 abuts the shoulder 56 between thesleeve and the cylindrical section 40. It should be noted that thecylindrical section 50 electrically insulates the cylindrical section 40from the opening 34 at the inner end of the bypass member 22 and sealsthe space between the section 48 in insulator 46 from the space in tube18.

The space between the outside surface of the section 50 and the insidesurface of the insulator 18 should be sealed in order to prevent archingbetween the shoulder 56 of the sleeve 20 and the opening 34. This can beaccomplished by means of a seal ring 55 provided between the bypassmember 22 and section 50 and also located between the inside end of tube18 and the opening 34.

Under normal operating conditions the prestrike are created on close-inwill be extinguished by the gas produced by the heat of the arc betweenthe extension 16 and the sleeve 18. When a fault condition is present onclose-in, the heat of the prestrike arc will produce an increased gaspressure of a sufficient magnitude to exceed the strength of thefrangible disc 52. Since the gas is confined in the space within thesleeve 20 and insulating tube 18, the sleeve 20 will act like a pistonbearing on the frangible disc 52 until the disc 52 breaks allowing thesleeve 20 to move rapidly into the space in the cylindrical section 48and away from the probe 12.

The sleeve 20 will move far enough to electrically engage the opening 34in the bypass member 22 setting up a bypass circuit through the member22 to the probe 12. The arc between the probe 12 and the sleeve 20 willbe immediately extinguished due to the new current path through theelectrical bypass member 22. The arc length is now reduced because thegap between the probe 12 and the opening 32 in the bypass element 22 andbetween the opening 34 in the bypass element and the sleeve 20 issmaller than the original gap between the probe 12 and the sleeve 20.This reduced arc length results in an immediate reduction in are energythereby preventing build up of gas pressure in the bushing.

FIGS. 3 and 4 In the embodiment of the invention shown in FIGS. 3 and 4,the gases produced by the arc quenching materials are confined within afrangible cylinder 60 which on rupture allows the pressure of the gasesto close an electric bypass circuit through an electrical bypass element62 between the bushing 58 and probe 80 in the terminator. Moreparticularly, the bushing 58 includes a housing 66 formed or molded froma dielectric material and having an axially extending passage 68. Thepassage 68 is closed at one end by means of an electrically conductivecap 70 mounted in a tubular element 72 which includes a threaded section73 at the inner end to threadedly receive the electrical contact 74. Thefrangible cylinder 60 is mounted on and closely surrounds the contact74. The cylinder 60 is formed as an integral part of the arc quenchingor snuffing cylinder 76 which has a reduced diameter to engage the arcextinguishing follower 78 and the electrically conductive probe 80 onthe terminator.

Means are provided in the bushing 58 for rapidly connecting the probe 80to the contact 74, in the event of a fault. Such means is in the form ofan electrically conductive element or sleeve 62 which is electricallyconnected at its inner end to the conductive tube 72 by means of aconductive support 82. The element 62 includes a plurality of fingers 84which are insulated from the contact 64 by the frangible cylinder 60.

The element 62 is spaced from a conductive cylinder 86 which is mountedwithin the passage 68 of the bushing and supports an arc snuffer 88located at the open end of the passage 68 in the housing 66. The arcsnuffer 88 has an internal diameter substantially equal to the outsidediameter of the follower 78 and probe 80.

Means are provided for clamping the probe 80 within the bushing toprevent blow back of the terminator in the event of a fault on close-in.Such means is in the form of a conductive clamp assembly 90 which ismounted on the end of the arc snuffer 76 in a position to engage theprobe 80. In this regard, the clamp 90 includes a number of elementshaving a radially outwardly tapered outer surface 92 positioned to rideon the inwardly tapered surface 94 on the conductive cylinder 86. Theclamp members are retained in the bushing by means of a seal ring 96.

As seen in FIG. 4, when an arc occurs as a result of a fault current, abuild up of pressure will occur within the frangible cylinder 60. Whenthis pressure exceeds the strength of the cylinder, the cylinder will besheared from the arc snuffer 76 and will be forced against the fingers84 of the conductive element 62. The fingers 84 will be blown outwardlyinto engagement with the conductive cylinder 86 forming an electricallyconductive bypass circuit through the clamp assembly 90, conductivecylinder 86, the fingers 84, the support member 82 and the conductivecylinder 72.

If the force of the gas within the conductive cylinder 86 is ofsufficient force to shear the arc snuffer 88 from the threadedconnection with the conductive cylinder 86, the clamp will be moved intotight gripping engagement with the probe 80. In this regard, as thepressure builds up on the seal 96, the elements of the clamp 90 will beforced against the end of the arc snuffer 88. When this force exceedsthe shear strength of the threaded section of the arc snuffer 88, thecylinder 86 will be moved axially outwardly from the bushing 58 allowingthe clamp members 98 to be cammed inwardly on the tapered cam surface 94on the conductive cylinder 86.

I claim:

1. A bushing for connecting electrical apparatus to the conductivemember of a high voltage cable terminator, said bushing including: adielectric housing having a passage, an electrically conductive contactpositioned within said passage, said contact being adapted toelectrically engage the conductive member in the terminator, a frangiblemember within said passage, means for connecting said contact to theelectrical apparatus, and electrical bypass means within said bushingfor connecting said contact to the conductive member when the pressureof the gas produced by the heat of the prestrike arc on close-in issufficient to break the frangible member.

2. The bushing according to claim 1 wherein said electrical bypass meanscomprises a cylindrical tube positioned with said passage and having asection at one end for electrically engaging the terminator and asection at the other end for electrically engaging said contact.

3. The bushing according to claim 2 including an insulating sleevepositioned with said cylindrical tube for supporting said contact foraxial movement within said passage.

4. The bushing according to claim 3 including a cylindrical section ofinsulating material mounted on said contact and being connected to saidfrangible member to confine the gases produced on prestrike to the inletend of said passage.

5. The bushing according to claim 1 wherein said electrical bypass meansincludes a cylindrical section to provide electrical communication withthe terminator and a sleeve mounted on said frangible member andextending into said cylindrical section whereby on rupture of saidfrangible member said sleeve will be forced into engagement with saidsection.

6. The bushing according to claim 5 including means within saidcylindrical section for clamping the terminator in said bushing onrupture of said frangible memher.

7. The bushing according to claim 6 wherein said clamping means respondsto the pressure of the gases produced on fault close in.

8. The bushing according to claim 1 wherein said frangible membersupports said contact within said passage.

9. The bushing according to claim 8 wherein said contact is movable intoengagement with said bypass means on rupture of said frangible member.

10. A voltage bushing for connecting electrical apparatus to theconductive probe of a high voltage cable terminator, said bushingincluding: a dielectric housing, an electrically conductive tubularcontact positioned within said housing, said contact being open at oneend to electrically engage the conductive probe in the terminator onclose-in, a gas evolving arc-quenching tube surrounding said contact andextending beyond the open end of said contact, a frangible member withinsaid housing, said frangible member confining the gases produced by theprestrike arc on close-in within said contact, means within said housingfor electrically connecting said contact to the electrical apparatus,and electrically conductive bypass means within said bushing forelectrically connecting the electrical apparatus to the conductive probewhen the pressure of the gas within the contact is sufficient to rupturethe frangible member and allow electrical engagement of saidelectrically conductive bypass means with said probe.

11. The bushing according to claim 10 wherein said electricalbypass-means comprises a hollow tubular member positioned within saidbushing and having a section at one end for electrically engaging theprobe and a section at the other end for electrically engaging saidcontact.

12. The bushing according to claim 10 wherein said frangible memberincludes a cylindrical section mounted on said contact and extendingpartially into said gas evolving tube.

13. The bushing according to claim 11 wherein said frangible memberincludes a cylindrical section surrounding one end of said contactextending through the section at the other end of the electrical bypassmeans and partially into the arc-quenching gas evolving tube.

14. The bushing according to claim 13 including means positioned betweenthe cylindrical section and the arc-quenching tube for sealing thecontact from the reduced diameter section of the electrical bypassmeans.

15. The bushing according to claim 10 wherein said electrical bypassmeans includes a cylindrical section to provide electrical communicationwith the probe and a sleeve surrounding said frangible member andextending into said cylindrical section whereby on rupture of saidfrangible member, said sleeve will be forced outwardly into engagementwith said cylindrical sectron.

16. The bushing according to claim 10 wherein said bypass means includesa clamp assembly positioned to respond to the increase of pressurewithin said bushing on rupture of said frangible member to clamp theprobe in the bushing.

17. The bushing according to claim 10 wherein said frangible member isintegral with and forms an extension of the said arc-quenching tube.

18. The bushing according to claim 15 including an arc-quenching sleevesecured to said cylindrical section at the open end of the passage insaid bushing and a clamp assembly mounted within said cylindricalsection and bearing against said arc-quenching sleeve, said assemblybeing positioned to respond to the pressure of the gas within thebushing on rupture of said frangible member to break said sleeve andmove into clamping position with respect to said probe.

1. A bushing for connecting electrical apparatus to the conductivemember of a high voltage cable terminator, said bushing including: adielectric housing having a passage, an electrically conductive contactpositioned within said passage, said contact being adapted toelectrically engage the conductive member in the terminator, a frangiblemember within said passage, means for connecting said contact to theelectrical apparatus, and electrical bypass means within said bushingfor connecting said contact to the conductive member when the pressureof the gas produced by the heat of the prestrike arc on close-in issufficient to break the frangible member.
 2. The bushing according toclaim 1 wherein said electrical bypass means comprises a cylindricaltube positioned with said passage and having a section at one end forelectrically engaging the terminator and a section at the other end forelectrically engaging said contact.
 3. The bushing according to claim 2including an insulating sleeve positioned with said cylindrical tube forsupporting said contact for axial movement within said passage.
 4. Thebushing according to claim 3 including a cylindrical section ofinsulating material mounted on said contact and being connected to saidfrangible member to confine the gases produced on prestrike to the inletend of said passage.
 5. The bushing according to claim 1 wherein saidelectrical bypass means includes a cylindrical section to provideelectrical communication with the terminator and a sleeve mounted onsaid frangible member and extending into said cylindrical sectionwhereby on rupture of said frangible member said sleeve will be forcedinto engagement with said section.
 6. The bushing according to claim 5including means within said cylindrical section for clamping theterminator in said bushing on rupture of said frangible member.
 7. Thebushing according to claim 6 wherein said clamping means responds to thepressure of the gases produced on fault close in.
 8. The bushingaccording to claim 1 wherein said frangible member supports said contactwithin said passage.
 9. The bushing according to claim 8 wherein saidcontact is movable into engagement with said bypass means on rupture ofsaid frangible member.
 10. A voltage bushing for connecting electricalapparatus to the conductive probe of a high voltage cable terminator,said bushing including: a dielectric housing, an electrically conductivetubular contact positioned within said housing, said contact being openat one end to electrically engage the conductive probe in the terminatoron close-in, a gas evolving arc-quenching tube surrounding said contactand extending beyond the open end of said contact, a frangible memberwithin said housing, said frangible member confining the gases producedby the prestrike arc on close-in within said contact, means within saidhousing for electrically connecting said contact to the electricalapparatus, and electrically conductive bypass means within said bushingfor electrically connecting the electrical apparatus to the conductiveprobe when the pressure of the gas within the contact is sufficient torupture the frangible member and allow electrical engagement of saidelectrically conductive bypass means with said probe.
 11. The bushingaccording to claim 10 wherein said electrical bypass means comprises ahollow tubular member positioned within said bushing and having asection at one end for electrically engaging the probe and a section atthe other end for electrically engaging said contact.
 12. The bushingaccording to claim 10 wherein said frangible member includes acylindrical section mounted on said contact and extending partially intosaid gas evolving tube.
 13. The bushing according to claim 11 whereinsaid frangible member includes a cylindrical section surrounding one endof said contact extending through the section at the other end of theelectrical bypass means and partially into the arc-quenching gasevolving tube.
 14. The bushing according to claim 13 including meanspositioned between the cylindrical section and the arc-quenching tubefor sealing the contact from the reduced diameter section of theelectrical bypass means.
 15. The bushing according to claim 10 whereinsaid electrical bypass means includes a cylindrical section to provideelectrical communication with the probe and a sleeve surrounding saidfrangible member and extending into said cylindrical section whereby onrupture of said frangible member, said sleeve will be forced outwardlyinto engagement with said cylindrical section.
 16. The bushing accordingto claim 10 wherein said bypass means includes a clamp assemblypositioned to respond to the increase of pressure within said bushing onrupture of said frangible member to clamp the probe in the bushing. 17.The bushing according to claim 10 wherein said frangible member isintegral with and forms an extension of the said arc-quenching tube. 18.The bushing according to claim 15 including an arc-quenching sleevesecured to said cylindrical section at the open end of the passage insaid bushing and a clamp assembly mounted within said cylindricalsection and bearing against said arc-quenching sleeve, said assemblybeing positioned to respond to the pressure of the gas within thebushing on rupture of said frangible member to break said sleeve andmove into clamping position with respect to said probe.